1. Mapping the Dark Matter in the Local Universe
CAASTRO
Mapping the Dark Matter in the Local Universe
Jeremy Mould
CAASTRO Inaugural Meeting
November 10, 2010 1

2. Mapping Dark Matter Use the gravitational effect of matter on light
Weak lensing
Measure the motions of galaxies induced by dark matter
Peculiar velocities

3. Couran Cove Workshop

4. The bullet cluster
Credit: X-ray: NASA/CXC/CfA/M.Markevitch et al.; Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.

5. Mapping the Dark Matter in the Local Universe
Conventional wisdom is that the distribution of dark matter in the Universe follows the distribution of galaxies.
Detailed models of the evolution of structure, such as the Millenium Simulation, embody that assumption.
Redshift surveys such as 2dFGRS and SDSS appear to be consistent with this relationship.
An observational test of the assumption is possible and is potentially very informative about the nature of dark matter.
Measurement of galaxy distances allows non-Hubble-expansion velocities of galaxies to be determined
How can these data can be integrated to provide a map of the dark matter on 100 Mpc scales ?
Both current projects (using the 6dF galaxy redshift survey) and future projects using the Australian Square Kilometre Array Pathfinder (due to operate in 2012) are relevant. 10

7. Virgocentric Flow

8. Density perturbations: Expanding Universe
Mini Friedman Universe
Lightman & Schechter 1990
Application to Virgocentric flow with
gave  = 0.1 +/- 0.03
Aaronson, Huchra, Mould, Schechter, Tully 1982

9. General relation between velocity field and density field
Continuity equation
Perturbation
Define a velocity potential Fv such that
where
and

10. Calculate the velocity field from the density field
It is also possible to go in the reverse direction and calculate the density field
from the velocity field
Smooth and integrate the velocity field to get the potential
Then recover the density field from the potential
Summary of cosmic flow (linear approximation)

11. Measuring galaxy peculiar velocities
Measure redshift (cz) and distance (r), get velocity

12. Tonry peculiar velocity model23

13. Virgocentric flow plus Great Attractor
Tonry et al 2001
Virgocentric flow plus Great Attractor
SGY
SGX Mpc

14. Tonry model radial velocities25

15. Density field reconstruction Dekel et al

16. 2MRS predicted flowfield
Lavaux & Tully 2010 27

17. Feldman, Watkins, Hudson 2010 Analysis of peculiar velocities

18. Expected distance to the dominant gravitational source

19. Cosmic Microwave Background WMAP 7 yr
Powerr

20. WALLABY - the ASKAP HI All-Sky Survey
ASKAP 36 x 12-m antennas (4072 sq m)
focal plane arrays
field-of-view 5.5 deg x 5.5 deg (= 30 sq deg)
GHz, i.e. ideal for large HI and 20-cm continuum surveys.
inner 30 antennas (3400 sq m) of ASKAP optimally arranged in a 2-km configuration, delivering an angular resolution of 30".
further six antennas at larger distances (max. baseline = 6-km), giving an excellent angular resolution of around 10".
A comparable Dutch survey is under consideration for the North

21. velocity resolution ~4 times better
WALLABY: Widefield ASKAP L-band Legacy All-sky Blind surveY
Principal Investigators: Baerbel S. Koribalski (ATNF) and Lister Staveley-Smith (UWA)
flux sensitivity ~20 times better than the HI Parkes All-Sky Survey (HIPASS)
velocity resolution ~4 times better
dwarf galaxies (MHI = 108 M*) out to a distance of ~60 Mpc,
massive galaxies (MHI = 6 x 109 M*) to ~500 Mpc
super-massive galaxies like Malin 1 (MHI = 5 x 1010 M*) to 1 Gpc.
mean sample redshift is expected to be z = 0.05 (200 Mpc).
For the ~3 x 104 galaxies expected to be larger than 1.5‘
simple structural, mass and angular momentum parameters.
automated parameter pipeline.

22. Typical 21 cm galaxy profile

23. Tully Fisher relation for spiral galaxies
Springob et all
Tully Fisher relation for spiral galaxies

24. The Skymapper Survey 39

25. How many of these are detectable, i > 45o, DV > 80 km/s ?

26. Constraints on large scale structure
Will the WALLABY
peculiar velocity
Survey require more
power on large
scales than WMAP ?
Does the dark matter follow the light distribution ? 41

27. CAASTRO